Please do not skip out on this test. My daughter did not get her PKU done until she was 6 months old(the peds missed her)Turned out she has congenitial hypothyroidism. Her endocrinologist was in shock that she was growing and hitting milestones-truly a miracle. Congenitial Hypothyroidism is the leading preventative cause of mental retardation. I cannot strsse how very important this simple test is!